Interference is a major source of concern for the designers of wireless communications systems. Interference can reduce the overall performance of the communications system and if severe enough, cause the communications system to fail altogether. Interference can come from other electrical and electronic devices operating in the general vicinity and from other devices in the same communications system, which are transmitting in the same (or adjacent) frequency band.
Interference from other devices in the same communications system can become a problem as designers of the communication system attempt to increase network capacity. For example, one way to increase network capacity is to increase frequency reuse, i.e., allow devices that are relatively close to one another to transmit in the same frequency band. In cellular communications systems, adjacent cell sites typically do not operate in the same frequency bands. However, through cell site sectoring, frequency reuse can be increased, therefore increasing network capacity. Unfortunately, when devices, which are close to one another, transmit in the same frequency band or in adjacent frequency bands, interference can occur. When devices transmit within the same frequency band, co-channel interference can occur, while adjacent channel interference can occur if devices transmit in adjacent bands if sufficient inter-band spacing is not provided.
Additionally, when multiple users are transmitting, the information may become mixed together and it may be necessary to extract one (or more) user's information from a received signal. For receivers with multiple antennas, linear schemes can be used to extract the desired information. The use of linear schemes in receivers with single antennas may be difficult if not impossible without the aid of additional signal manipulation.
In a GSM (Global System for Mobile Telephony) wireless communications system, for example, information is transmitted in transmission bursts, wherein each transmission burst may consist of two packets of data bits with a 26 bit mid-amble located in between the two packets. According to the GSM technical standards, one of eight possible training sequence codes (TSC) can be used as the mid-amble. In GSM communications systems, attempts to increase system capacity have resulted in increased co-channel and adjacent channel interference. Several attempts to reduce interference have been proposed. Most of the prior art relies on using at least two antennas at the receiver to suppress interference. However, due to cost reasons there is generally only one antenna in GSM handsets. With a single antenna at the receiver, one single antenna interference cancellation (SAIC) technique is to use the joint MLSE receiver.
A disadvantage of the prior art is that the schemes which provide significant performance gain require the channel information of the interferers. This may not be available since in general the identity of the interferers is unknown. In a synchronous network, this may require an algorithm capable of detecting the presence and identity of the interferer(s). In an asynchronous network, attaining such information is generally infeasible.